Dispersing agent

ABSTRACT

Dispersions of pigment, such as calcium carbonate, titanium dioxide and types of clay, can be effectively stabilized by the use of carboxyl-containing fructan in an amount of 0.05-10% by weight, based on the dispersion, which fructan contains 0.5-3 carboxyl groups per mono-saccharide unit. The carboxyalkyl groups are in particular carboxymethyl groups, but the carboxyl groups can also be carboxyl groups obtained entirely or partially by oxidation. The carboxymethylfructan gives results which are comparable to or better than those obtained with the polyacrylates which are less desirable from the standpoint of health and environment.

This Application is the National Phase of PCT/NL99/000359 filed,06/09/1999.

The invention relates to the use of specific fructan derivatives as adispersing agent.

Dispersed solid particles usually have the tendency to flocculate and/orto precipitate. A dispersing agent prevents this flocculation and as aresult stabilises the dispersion. In addition, a dispersing agent lowersthe viscosity of the dispersion. As a result the dispersions can bepumped or processed more easily at higher concentrations of solidparticles. This is important both from the technical and from theeconomic standpoint.

Phosphates and polyphosphates, such as sodium hexametaphosphate, arewidely used as inorganic dispersing agents. These inorganic agents havea good dispersing action but have the disadvantage that they are notstable to hydrolysis. As a result, the viscosity of the dispersion willincrease in the course of time.

Organic dispersing agents used are polymers and copolymers of acrylicacid and methacrylic acid having a molecular weight of 5,000 to 100,000.For instance, dispersions of more than 50% by weight of solid particles(such as clay particles) with a polyacrylate as dispersing agent aredescribed in WO 95/25146. DE-A 2 700 444 describes the use of copolymersof maleic acid, JP-A-56-115630 that of unsaturated sulphonic acids andEP-A 705 893 that of phosphonocarboxylic acids as dispersing agents oras deflocculants.

The disadvantage of the organic dispersing agents used to date is thatthey are all based on petrochemical, and thus non-renewable, rawmaterials. Furthermore, these substances are poorly degradable and/ortoxic to surface water or soil. There is therefore a need for organicdispersing agents which score better than the known petrochemicalproducts with regard to these aspects.

It has been found that carboxyl-containing fructans and salts thereofmeet this need. These derivatives have a dispersing action for solidsubstances, in particular pigments, are biodegradable and are non-toxic.The invention therefore relates to a method for the preparation ofdispersions and to dispersions obtainable in this way, as described inthe appended claims.

In this context fructans are understood to include all oligosaccharidesand poly-saccharides which have a majority of anhydrofructose units. Thefructans can have a poly-disperse chain length distribution and can bestraight-chain or branched. The fructan can contain mainly β-2,6 bonds,as in levan. Preferably the fructan contains mainly β-2,1 bonds, as ininulin.

In this context carboxyl-containing fructans are understood to be aderivative of inulin or another fructan that contains 0.3-3 carboxylgroups per anhydrofructose unit. In particular the derivative containsat least 0.8 carboxyl groups per anhydrofructose unit. The carboxylgroups can be present in the form of carboxyalkyl groups, such ascarboxymethyl, carboxyethyl, dicarboxymethyl or carboxyethoxycarbonylgroups. These can be obtained by etherification of the fructan in aknown manner. The carboxyl groups can also be present in the form ofoxidised hydroxymethylene or hydroxymethyl groups. Mixed carboxyfructanscan also be used. Preferably, the number of carboxymethyl groups isgreater than the number of other carboxyl groups. Carboxymethylinulin(CMI) is the most preferred.

Carboxymethylinulin (CMI) with a DS (degree of substitution) of 0.15-2.5is disclosed in WO 95/15984 and in the article by Verraest et al. inJAOCS, 73 (1996) pp. 55-62. It is prepared by reaction of a concentratedsolution of inulin with sodium chloroacetate at elevated temperature.Carboxylethylinulin (CEI) is disclosed in WO 96/34017. The oxidation ofinulin is, for example, disclosed in WO 91/17189 and WO 95/12619 (C3-C4oxidation, leading to dicarboxyinulin, DCI) and WO 95/07303 (C6oxidation). In the case of mixed carboxyl derivatives the inulin canhave been first carboxymethylated and then oxidised or (preferably) theother way round.

The carboxyl-containing fructan has an average chain length (=degree ofpolymerisation, DP) of at least 3, rising to about 1000. Preferably, theaverage chain length is 6-60 monosaccharide units. The fructan canoptionally have been subjected to a reduction treatment beforehand inorder to remove reducing groups.

Modified fructan derivatives which according to the invention can beconverted to carboxyalkylfructan are, for example, fructans in which thechain length has been enzymatically extended, and fructan hydrolysisproducts, that is to say fructan derivatives having a shortened chain,and fractionated products having a modified chain length. Fractionationof fructans such as inulin can be effected by, for example, lowtemperature crystallisation (see WO 94/01849), column chromatography(see WO 94/12541), membrane filtration (see EP-A 440 074 and EP-A 627490) or selective precipitation with alcohol. Prior hydrolysis toproduce shorter fructans can, for example, be effected enzymatically(endo-inulinase), chemically (water and acid) or by heterogeneouscatalysis (acid column). Hydroxyalkylated and/or cross-linked fructansalso come into consideration for use in the method according to theinvention after carboxyalkylation and, if appropriate, oxidation.

The carboxymethylfructan can be used in the form of the purifiedsubstance, but use can also be made of the technical grade productobtained directly by carboxymethylation. Specifically, it has been foundthat any impurities, such as glycolic acid and diglycolic acid, have noadverse effects on the action of the CMI. It is possible to make use ofthe free acid, but also of a salt, such as the sodium, potassium orammonium salts.

The solid to be dispersed or suspended can be any solid which issufficiently chemically inert to be able to be dispersed or suspended inwater. The particles are usually inorganic and insoluble in water.Examples are talc, barite, calcium carbonate, mica, kaolin, bentoniteand other types of clay, zinc oxide, calcium sulphate, zeolite, carbon,haematite and the like. The carboxyfructans can be used as dispersingagents for soluble or semi-soluble solids.

Dispersions of calcium carbonate and titanium dioxide can be used inpaints and other coating compositions. Other widely used pigments whichcan be dispersed using the carboxyfructans according to the inventionare, for example, iron oxide, carbon black and aluminium stearate. Thepigment can also be a corrosion-inhibiting pigment, such as red lead,zinc oxide, zinc powder or aluminium powder, citrates and the like. Itis also possible to prepare bentonite dispersions, which can be used assofteners in, for example, detergents and weighting materials indrilling muds; Furthermore, the carboxyfructans can be used for a widevariety of dispersions of low viscosity, for coating paper. Pigmentswhich can be used for this purpose are, for example, kaolin, satinwhite, calcium carbonate and talc. Other uses are e.g. in dispersingmining products.

For rapid dispersion the particle size of the solids is preferably assmall as possible, preferably less than 1 mm and in particular between 1and 50 μm. The solids concentration is 1-90% by wt based on the totalweight of the dispersion. From the economic standpoint, theconcentration is at least 30% by wt rising to, for example, 80% by wt.

The carboxyl-containing fructan can first be mixed with the pigment (orother substance to be dispersed or to be suspended) and then added tothe water, or it can first be added to the water before the pigment isadded with vigorous stirring.

The quantity of carboxyl-containing fructan, in particular CMI, is ingeneral between 0.05 and 10% by wt, in particular between 0.2 and 2% bywt. It is also possible to use mixtures of the carboxyl-containingfructan and other dispersing agents, such as polyacrylates orphosphonates, preferably in a ratio of at least I partcarboxyl-containing fructan to one part other agent. The pH of thedispersion system is usually neutral to slightly. alkaline (pH 6-12);the pH is often above 7. If necessary, other solvents, such as alcohols,can be added to the water; however water usually suffices.

The carboxyl-containing fructans have a dispersing action, expressed innumber of mols carboxyl groups that is required per tonne dry pigment(see WO 97/10308), which is as good as or even better than that ofpolyacrylates.

EXAMPLES Example 1

CMI with a DS (degree of substitution; average number of substituentsper monosaccharide unit) of 2.4 and 100% DCI were compared with acommercial polyacrylate (PA, mol. wt. 4500) that is used for dispersingcalcium carbonate in the paints industry. An initial dosage ofdispersing agent was added to 250 g CaCO₃ (Socal P2, Solvay) in 150 gwater. Small dosages of dispersing solution were then added to thedispersion. The concentration of the dispersing solutions was 1% solids.After each addition the viscosity of the dispersion was measured at 25°C. using a Brookfield viscometer. The results are given in Table 1.

TABLE 1 % Dispersing agent with Viscosity (Pas) respect to pigment CMIDCI PA (comp.) 0 16.3 16.3 16.3 0.05 14.2 11.2 16.5 0.075 12.2 9.3 16.60.10 8.8 7.1 11.2 0.125 5.5 4.7 5.2 0.15 2.9 3.2 4.2

Example 2

The viscosity of the following paint formulation (parts by weight) wasdetermined 1 day and 28 days after making up and storing at 50° C.

water 274.5 Tylose MH 30000 yp2 3 NaOH 10% 1 Calgon N 10% 5 TionaRCL-535 30 Socal P2 120 Omyacarb 2 GU 120 Omyacarb 5 GU 280 IndustrieSpezial 100 Mowilith LDM 1871 60 Mergal K9N 2 Byl 033 2 Dispersing agent30% in water 2.5

The results are as follows:

Viscosity (mPas) Dispersing agent After 1 day After 28 days PolyacrylateA (comparative) 5000 4600 Polyacrylate B (comparative) 5500 5700 CMI DS1.5 6100 7600 CMI DS 2.4 4800 4600 DCI 60% 600 5700 DCI 100% 5500 5700

Example 3

Various CMI products were compared with a commercial polyacrylate in thedispersion of calcium sulphoaluminate of the formula3CaOAl₂O₃.3CaSO₄.32H₂O. The concentration of the slurry was 50%. It wasinvestigated how much dispersing agent at 30° C. is needed to reduce theviscosity of the slurry to 25 mPas (Brookfield viscometer 60 rpm). Itcan be seen from the results given below that compared with thepolyacrylate in particular the CMI products with a relatively low DSrequire fewer carboxyl groups to lower the viscosity to the set value.

Consumption % Carboxyl groups % Dispersing agent based on wet slurrybased on wet slurry CMI DS 0.5 0.94 0.16 CMI DS 1.0 0.82 0.23 CMI DS 1.50.83 0.30 CMI DS 2.5 0.90 0.42 Polyacrylate A (comp.) 0.44 0.31

Example 4

Effect of the carboxyl content of CMI on dispersion of kaolin.

An initial dosage of dispersing agent was added to 269.4 g kaolin in115.5 g water. Small dosages of dispersing solution were then added tothe dispersion. The concentration of the dispersing solutions was 40%solids. After each addition the viscosity of the dispersion was measuredat 25° C. using a Brookfield viscometer. The results are given in theappended figure.

What is claimed is:
 1. A method for preparing a stable dispersion ofsolids in an aqueous medium using a polycarboxy compound, characterisedin that a carboxyl-containing fructan that contains 0.3-3 carboxylgroups per monosaccharide unit is incorporated in the medium and/or inthe solids.
 2. A method according to claim 1, wherein 0.05-10% by wt ofthe carboxyl-containing fructan is used, based on the solid to bedispersed.
 3. A method according to claim 1, wherein thecarboxyl-containing fructan contains at least 0.8 carboxyl group permonosaccharide unit.
 4. A method according to claim 1, wherein thecarboxyl-containing fructan contains 0.7-2.5 carboxymethyl groups permonosaccharide unit.
 5. A method according to claim 1, wherein thecarboxyl-containing fructan is a carboxymethylinulin having an averagedegree of polymerisation of 6-60.
 6. A method according to claim 1,wherein the solid to be dispersed is a pigment or a type of clay.
 7. Amethod according to claim 1, wherein a product obtained directly bycarboxyalkylation of a fructan is used.
 8. A method according to claim1, wherein a purified carboxyalkylfructan is used.
 9. A stabledispersion of a pigment in an aqueous medium, which contains 1-90% by wtof the pigment and 0.002-5% by wt of a carboxyl-containing fructan thatcontains 0.3-3 carboxyl groups per monosaccharide unit, the percentagesby weight being based on the total weight of the dispersion.
 10. Astable dispersion according to claim 9, which contains 30-80% by wt ofthe pigment and 0.015-3% by wt of the carboxyl-containing fructan, basedon the dispersion.